Clear disk cache after read #6396

xzfc · 2025-04-16T17:44:20Z

Related: #6323.

Consider this simplified example:

fn read_data(path: &Path) -> io::Result<Vec<u8>> {
    let file = File::open(path)?;
    let reader = BufReader::new(file);
    let data = Vec::new();
    reader.read_to_end(&mut data)?;
    data
}

The problem with this code is that after calling this function, the file contents is stored twice in the memory: once as Vec<u8> (as anonymous memory), and once implicitly as OS file cache, making it more likely to evict other files from the cache.

Particularly, after reproducing #6323, I've found that quantized vectors and id tracker files are still in the OS file cache when the mmaped index cache gets evicted. Since we are unlikely to read quantized vectors again, we'd better to avoid polluting the OS file cache.

This PR adds a new wrapper around File, OneshotFile, that calls posix_fadvise(…, POSIX_FADV_DONTNEED) when the file is closed. Not ideal, but should improve the situation a bit.

coderabbitai · 2025-04-16T17:47:20Z

📝 Walkthrough

Walkthrough

This set of changes introduces a new fadvise module in the lib/common/memory crate that provides functionality for managing file access patterns and explicit cache eviction using the posix_fadvise system call on supported platforms. A new build script (build.rs) is added to conditionally enable compilation of posix_fadvise-dependent code based on the target OS and environment. The core addition is the OneshotFile struct, a wrapper around std::fs::File that applies sequential and no-reuse access hints and supports explicit cache dropping via drop_cache(). The existing clear_disk_cache function is removed from the madvise module and reimplemented in the new fadvise module. All imports and usages of clear_disk_cache across the codebase are updated to reference the fadvise module. Additionally, several components now use OneshotFile for file reading and explicitly drop file caches after operations, replacing previous uses of standard File.

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timvisee

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Reviewing files that changed from the base of the PR and between 51e227b and 6414477.

📒 Files selected for processing (3)

lib/quantization/src/encoded_storage.rs (2 hunks)
lib/segment/src/id_tracker/mutable_id_tracker.rs (2 hunks)
lib/segment/src/vector_storage/chunked_vectors.rs (3 hunks)

🚧 Files skipped from review as they are similar to previous changes (3)

lib/segment/src/vector_storage/chunked_vectors.rs
lib/quantization/src/encoded_storage.rs
lib/segment/src/id_tracker/mutable_id_tracker.rs

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GitHub Check: test-snapshot-operations-s3-minio
GitHub Check: test-shard-snapshot-api-s3-minio
GitHub Check: test-low-resources
GitHub Check: test-consistency
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GitHub Check: Basic TLS/HTTPS tests
GitHub Check: rust-tests (macos-latest)
GitHub Check: integration-tests
GitHub Check: lint
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Actionable comments posted: 0

🧹 Nitpick comments (1)

lib/segment/src/id_tracker/mutable_id_tracker.rs (1)

659-675: Consider using OneshotFile for loading versions as well.

The load_versions function still uses a standard File while the load_mappings function was updated to use OneshotFile. For consistency and to fully implement the cache optimization strategy, consider updating this function as well.

-    let file = File::open(versions_path)?;
+    let file = OneshotFile::open(versions_path)?;

     let file_len = file.metadata()?.len();
     if file_len % VERSION_ELEMENT_SIZE != 0 {
         log::warn!(
             "Corrupted ID tracker versions storage, file size not a multiple of a version, assuming automatic recovery by WAL"
         );
     }
     let version_count = file_len / VERSION_ELEMENT_SIZE;

     let mut reader = BufReader::new(file);

-    Ok((0..version_count)
+    let result = Ok((0..version_count)
         .map(|_| reader.read_u64::<FileEndianess>())
-        .collect::<Result<_, _>>()?)
+        .collect::<Result<_, _>>()?);
+    
+    // Drop the cache after reading
+    let file = reader.into_inner();
+    file.drop_cache()?;
+    
+    result

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📥 Commits

Reviewing files that changed from the base of the PR and between 751fb5a and e5c5748.

⛔ Files ignored due to path filters (1)

Cargo.lock is excluded by !**/*.lock

📒 Files selected for processing (23)

lib/common/memory/Cargo.toml (2 hunks)
lib/common/memory/build.rs (1 hunks)
lib/common/memory/src/fadvise.rs (1 hunks)
lib/common/memory/src/lib.rs (1 hunks)
lib/common/memory/src/madvise.rs (0 hunks)
lib/gridstore/src/bitmask/gaps.rs (1 hunks)
lib/gridstore/src/bitmask/mod.rs (1 hunks)
lib/gridstore/src/page.rs (1 hunks)
lib/quantization/src/encoded_storage.rs (2 hunks)
lib/segment/src/id_tracker/mutable_id_tracker.rs (3 hunks)
lib/segment/src/index/field_index/full_text_index/mmap_inverted_index/mod.rs (1 hunks)
lib/segment/src/index/field_index/geo_index/mmap_geo_index.rs (1 hunks)
lib/segment/src/index/field_index/map_index/mmap_map_index.rs (1 hunks)
lib/segment/src/index/field_index/mmap_point_to_values.rs (1 hunks)
lib/segment/src/index/field_index/numeric_index/mmap_numeric_index.rs (1 hunks)
lib/segment/src/index/hnsw_index/hnsw.rs (1 hunks)
lib/segment/src/vector_storage/chunked_mmap_vectors.rs (1 hunks)
lib/segment/src/vector_storage/chunked_vectors.rs (3 hunks)
lib/segment/src/vector_storage/dense/dynamic_mmap_flags.rs (1 hunks)
lib/segment/src/vector_storage/dense/memmap_dense_vector_storage.rs (1 hunks)
lib/segment/src/vector_storage/quantized/quantized_vectors.rs (1 hunks)
lib/sparse/src/index/inverted_index/inverted_index_compressed_mmap.rs (1 hunks)
lib/sparse/src/index/inverted_index/inverted_index_mmap.rs (1 hunks)

💤 Files with no reviewable changes (1)

lib/common/memory/src/madvise.rs

🧰 Additional context used

🧬 Code Graph Analysis (15)

lib/gridstore/src/bitmask/mod.rs (2)

lib/segment/src/vector_storage/quantized/quantized_vectors.rs (1)

lib/segment/src/vector_storage/dense/memmap_dense_vector_storage.rs (1)

lib/gridstore/src/page.rs (2)

lib/segment/src/index/hnsw_index/hnsw.rs (1)

lib/segment/src/index/field_index/mmap_point_to_values.rs (2)

lib/segment/src/vector_storage/chunked_mmap_vectors.rs (2)

lib/sparse/src/index/inverted_index/inverted_index_compressed_mmap.rs (2)

lib/segment/src/index/field_index/numeric_index/mmap_numeric_index.rs (2)

lib/segment/src/index/field_index/map_index/mmap_map_index.rs (2)

lib/segment/src/index/field_index/geo_index/mmap_geo_index.rs (2)

lib/quantization/src/encoded_storage.rs (1)

lib/gridstore/src/bitmask/gaps.rs (2)

lib/common/memory/src/lib.rs (1)

lib/segment/src/id_tracker/mutable_id_tracker.rs (1)

⏰ Context from checks skipped due to timeout of 90000ms (13)

GitHub Check: Basic TLS/HTTPS tests
GitHub Check: test-snapshot-operations-s3-minio
GitHub Check: test-shard-snapshot-api-s3-minio
GitHub Check: test-low-resources
GitHub Check: test-consistency
GitHub Check: rust-tests (macos-latest)
GitHub Check: test-consensus-compose
GitHub Check: rust-tests (windows-latest)
GitHub Check: integration-tests-consensus
GitHub Check: rust-tests (ubuntu-latest)
GitHub Check: integration-tests
GitHub Check: lint
GitHub Check: storage-compat-test

🔇 Additional comments (32)

Copilot

Pull Request Overview

This PR addresses the file cache pollution issue by replacing the previous disk cache clearing mechanism with a new fadvise‐based implementation using an OneshotFile wrapper. Key changes include:

Replacing all usages of memory::madvise::clear_disk_cache with memory::fadvise::clear_disk_cache.
Updating file read operations to use OneshotFile::open and invoking drop_cache() to clear the OS file cache after reading.
Adding a new fadvise module along with necessary build script and dependency adjustments.

Reviewed Changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lib/segment/src/vector_storage/dense/memmap_dense_vector_storage.rs	Updated clear_disk_cache import to use fadvise module.
lib/segment/src/vector_storage/dense/dynamic_mmap_flags.rs	Updated ordering of import for clear_disk_cache to fadvise.
lib/segment/src/vector_storage/chunked_vectors.rs	Replaced File::open with OneshotFile::open and added drop_cache call.
lib/segment/src/vector_storage/chunked_mmap_vectors.rs	Updated clear_disk_cache import to use fadvise module.
lib/segment/src/index/hnsw_index/hnsw.rs	Updated clear_disk_cache import to use fadvise module.
lib/segment/src/index/field_index/numeric_index/mmap_numeric_index.rs	Updated clear_disk_cache import to use fadvise module.
lib/segment/src/index/field_index/mmap_point_to_values.rs	Updated clear_disk_cache import to use fadvise module.
lib/segment/src/index/field_index/map_index/mmap_map_index.rs	Updated clear_disk_cache import to use fadvise module.
lib/segment/src/index/field_index/geo_index/mmap_geo_index.rs	Updated clear_disk_cache import to use fadvise module.
lib/segment/src/index/field_index/full_text_index/mmap_inverted_index/mod.rs	Updated clear_disk_cache import to use fadvise module.
lib/segment/src/id_tracker/mutable_id_tracker.rs	Replaced File::open with OneshotFile::open and added drop_cache call.
lib/quantization/src/encoded_storage.rs	Replaced File::open with OneshotFile::open and added drop_cache call.
lib/gridstore/src/page.rs	Updated clear_disk_cache import to use fadvise module.
lib/gridstore/src/bitmask/mod.rs	Updated clear_disk_cache import to use fadvise module.
lib/gridstore/src/bitmask/gaps.rs	Updated clear_disk_cache import to use fadvise module.
lib/common/memory/src/madvise.rs	Removed clear_disk_cache implementation.
lib/common/memory/src/lib.rs	Added export for new fadvise module.
lib/common/memory/src/fadvise.rs	New module that implements clear_disk_cache and the OneshotFile wrapper.
lib/common/memory/build.rs	New build script to enable posix_fadvise support conditionally.
lib/common/memory/Cargo.toml	Added new dependency on delegate.

* Move clear_disk_cache to memory::fadvise * Add memory::fadvise::OneshotFile * Use OneshotFile

xzfc added 2 commits April 16, 2025 17:08

Move clear_disk_cache to memory::fadvise

41576d8

Add memory::fadvise::OneshotFile

f51fc01

xzfc requested review from timvisee and generall April 16, 2025 17:44

coderabbitai bot reviewed Apr 16, 2025

View reviewed changes

xzfc force-pushed the fadvise-after-read branch from e5c5748 to 51e227b Compare April 16, 2025 17:58

Use OneshotFile

6414477

xzfc force-pushed the fadvise-after-read branch from 51e227b to 6414477 Compare April 16, 2025 18:05

github-actions bot mentioned this pull request Apr 16, 2025

Flaky test multivector_filtrable_hnsw_test::test_multi_filterable_hnsw::case_5_recobestscore_eq #6318

Closed

xzfc requested a review from Copilot April 16, 2025 23:10

Copilot AI reviewed Apr 16, 2025

View reviewed changes

generall approved these changes Apr 17, 2025

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generall merged commit 9fedc65 into dev Apr 17, 2025
17 checks passed

generall deleted the fadvise-after-read branch April 17, 2025 08:57

pull bot pushed a commit to kp-forks/qdrant that referenced this pull request Apr 21, 2025

Clear disk cache after read (qdrant#6396)

1f805b6

* Move clear_disk_cache to memory::fadvise * Add memory::fadvise::OneshotFile * Use OneshotFile

coderabbitai bot mentioned this pull request Jul 14, 2025

Fix mmap payload index load, load in stages #6860

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Clear disk cache after read #6396

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xzfc commented Apr 16, 2025

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coderabbitai bot commented Apr 16, 2025 •

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